Furnace and heat exchanger for heating gases



Jan. 30, 1962 J. o. DONNISON 3,018,773

FURNACE AND HEAT EXCHANGER FOR HEATING GASES Filed Aug. 28, 1958 v 3Sheets-Sheet l /N l/E N TOP John O/daker Donn/son BYW ATTORNEY Jan. 30,1962 J. o. DONNISON 3,018,773

FURNACE AND HEAT EXCHANGER FOR HEATING GASES Filed Aug. 28, 1958 5Sheets-Sheet 2 IN l/E N 70/? John O/daker Donn/L500 BY ffM A 7'7'OPNEYJan. 30, 1962 J. o. DONNISON 3,013,773

FURNACE AND HEAT EXCHANGER FOR HEATING GASES Filed Aug. 28, 1958 3Sheets-Sheet 3 3' wvcwrop John O/daker Donn/son BY 4W A TTOPNEY UnitedStates Patent 3,018,773 FURNACE AND HEAT EXCHANGER FOR HEATING GASESJames Oldaker Donnison, Earls Colue, England, assignor to Air ExchangersLimited, London, England, a British company Filed Aug. 28, 1958, Ser.No. 757,811 Claims priority, application Great Britain Aug. 30, 1957 6Claims. (Cl. 126-110) This invention relates to a heater of thecontinuous, as distinct from the regenerative, type for indirectlyheating air or other gas from combustion gases, that is to say by heatexchange through a wall which separates the air or other gas to beheated from the combustion gases. Its purpose is to provide aconstruction which is simple to manufacture and easy to clean. A furtherpurpose is to present low resistance to flow so that the gas may bepropelled through the heater by an axial flow fan. Other purposes are toenable the temperature of the issuing gas to be varied without impairingthe efficient combustion of the fuel, and to minimise loss of heatotherwise than to the gas to be heated.

A heater according to the invention comprises an elongated casing ofsubstantially constant cross section, an elongated main baflle ofsimilar but smaller cross section and of shorter length than said casingand longitudinally disposed Within said casing spaced therefrom allround, a corrugated wall in the space between said main bafile and saidcasing and occupying the greater part of the space peripherally and setwith its ridges and valleys longitudinally, its ridges being at leastnearly in contact with said casing and its valleys being at least nearlyin contact with said main bafile, said corrugated wall extending at bothends beyond said main bafile but not beyond-the ends of said casing,means forming a combustion chamber discharging combustion gases towardsone end of said main bafile, said main baffle being imperforate towardsthe combustion chamber and towards said corrugated wall so that thecombustion gases are directed by it into the space inside saidcorrugated wall and outside said main baffle, means at both ends of saidcorrugated wall closing the ends of the space between said corrugatedwall and said main bafile and thereby restricting the combustion gasesdischarged by said combustion chamber to the space inside saidcorrugated wall without impeding flow of gas to be heated in the spacebetween said corrugated wall and said casing, and lateral passagesextending radially from-the space within said corrugated wall and to anopening in said casing for carrying the combustion gases out of saidcasing, said passages being located in the space between said mainbaffle and said casing in that part of the periphery not occupied bysaid corrugated wall and extending substantially within the same lengthas said corrugated wall, and spaces being left between said passages forthe flow of gas to be heated in parallel with that flowing between saidcorrugated wall and said casing.

Desirably the main baflle incorporates a transverse plate at the endnearer the combustion chamber and a baffle wall extending lengthwisefrom the plate over the end of which the combustion gases pass to enterthe hollow space bounded by the baffle wall, the part of the battle wallopposite the lateral passages being cut back to permit outflow of thecombustion gases into the passages.

In eflFect the corrugated wall in conjunction with the central bafileand the casing divides the space over which it extends circumferentiallybetween the main baffle and the outer casing into a series ofsubstantially triangular sectioned passages for the gas to be heated onthe outside of the wall, alternating with a second series ofsubstantially triangular sectioned passages for combustion gases on theinside of the wall, but while the wall hermetically separates the gas tobe heated from the combustion gases, since the flow in each series ofpassages is in parallel the passages constituting either series need notbe actual tubes hermetically separated from one another.

Thus it is convenient to use the valleys of the corrugated wall (whichmay be made of metal sheets folded substantially into V form withrounded apices and with the outer edges of adjacent sheets welded orsimilarly secured together) to support the bafile either by contactingwith it or through narrow intermediate rings, and it is also convenientto allow only a few of the ridges to contact the inside of the casing tolocate the corrugated wall, leaving the others clear of the casing, sothat the wall can be inserted or withdrawn without undue frictionalresistance or risk of jamming.

The outward radial flow of the combustion gases may be through passagesdefined by walls over the opposite sides of which passes a proportion ofthe gas to be heated, so that the flow of gas to be heated isdistributed substantially all round the space between the main baffleand the outer casing. This proportion of the gas to be heated may flowthrough actual tubes of substantially triangular section formed of metalsheets folded into V form so shaped and spaced as to leave radialpassages of substantially constant width between them for the combustiongases, these tubes being completed by sheet metal closures extendingbetween the outer edges of each V form sheet. The lateral passages mayextend over the same length as the corrugated wall so that combustiongases have access to them from the combustion chamber end but theyshould then be provided with baffles to prevent too great a proportionof combustion gases from taking the short gas path so presented.

The invention will be further described with reference to theaccompanying drawings which illustrate an example of embodiment and amodification.

FIGURE 1 is a longitudinal section of the heater without the means forpropelling the gas to be heated through it.

FIGURE 2 is an end view of FIGURE 1, the left-hand part being in sectiontaken on the line II-II of FIG- URE 1.

FIGURE 3 is a diagrammatic View of the modification which provides forthe admixture of relatively unheated gas with heated gas.

In the example illustrated in FIGURE 1 and 2 the casing of the heater isa sheet metal cylinder 11, to flanges 12 of which are bolted sheet metalfeet or brackets 13, upon which the heater may stand with the cylinderaxis horizontal or by the aid of which it may be hung from an overheadframe, or attached to a vertical or inclined frame with its axis at anydesired inclination to suit the duct system it supplies.

Within this casing 11 is a sheet metal corrugated wall of large surfaceseparating the space for the products of combustion from the spacethrough which flows the gas to be heated. In effect this wall forms twoseries of passages having the form of incomplete tubes. It is built ofsteel sheets 14 folded about their midlines into V form with a roundedvalley at 15, and disposed peripherally around the great part, say 270,from A to A FIGURE 2, of a wide tubular bafile wall 16 concentric withcasing 11, with their folds parallel to its axis i.e. lengthwise andwelded or similarly joined each to its neighbours along their outeredges as at 17 to form ridges. In this example the valleys 15 do notcontact the wall 16 directly but are secured to narrow intermediaterings 18, two of which at the ends of the wall 16 serve to support themain baffle of which the wall 16 forms part. Each sheet with a sectionof the baflle wall 16 Patented Jan. 30, 1952- forms a passage 19 ofsubstantially triangular crosssection on the inside of the zig-zag Wallfor the passage of combustion gases; and the remainder of the interiorof the casing outside the corrugated wall is available for the passageof gas to be heated. This also is divided into passages 21 ofsubstantially triangular cross-section, but these are not closed tubesfor only a few of the sheets need to extend to the casing, say, at threeor more symmetrically spaced axial lines, to support the Wholecorrugated dividing wall in readily removable fashion. Two such lines ofcontact are indicated in FIGURE 2 at 22. The triangular passages 18 forthe combustion gases are closed at their ends by Welded-on transversewalls 23, 24 of corresponding shape so that the passage 21 are left openat their ends. It will be clear that since the flow both of thecombustion gases and the gas to be heated in the triangular sectionpassages 19, 21 respectively is in parallel, the fact that thesepassages are not closed tubes does not matter. It will be understoodthat the corrugated wall constituted by the V form sheets 14 does form ahermetic barrier however between the gas to be heated and the combustiongases.

The combustion gases come from a combustion chamber described belowwhich joins the wall 24 so restricting the gases to the inside of thecorrugated wall. The bafiie wall 16 terminates short of the wall 24 andis closed by a transverse plate 25 so that the combustion gases arediverted into the passages 19.

At the outlet end, the baflle wall 16 terminates at 26 short of the endsof the triangular passages 19 so that the combustion gases from thesepassages 19 pass over the end of the wall 16 and into the hollow spacewithin it. From here over the remainder of the circle (i.e. 90 if thecorrugated Wall occupies 270) and over a somewhat greater axial lengththe wall 16 is cut back at 27 oppositc an outlet for the combustiongases formed by a number of narrow radial lateral passages 28 formedbetween steel sheets 29 folded into V form with rounded valleys 31 whichare similarly located to the valleys 15 but with the limbs of adjacentsheets parallel, see FIG- URE 2. The gases pass through these lateralpassages out of the casing 11 into a collecting chamber 32 on theoutside of the casing 11 and which in turn forms a flue collar 33. Toenable the whole peripheral space or annulus between the casing 11 andbafile wall 16 to be used, the edges of the sheets 29 are joined bysheet metal closures 34 to form complete tubes of substantiallytriangular section along which flows a proportion of the gas to beheated corresponding to the part of the annulus in which they lie, andthe lateral passages are closed at their ends to prevent escape ofcombustion gases into the gas to be heated As shown the sheets 29 andthus the passages 28 are of the same length as the corrugated wall sothat the Wall 24 serves as the end closure of these passages 28. Also toprevent an undue proportion of the combustion gas from taking the shortgas path presented by those passages 28 from the combustion chamber endto the flue, two further bafiles 35, 36 cut down the section of theshort path. The assembly of the sheets 29 and closures 34 isconveniently secured to the casing by flanges 37 bolted in place.

The outer end of the central space in line with the baflie wall 16 isclosed, but to permit access to the interior the door is removable. Itmay comprise a disc 38 and a conical frustum 39 bolted together, thebase of the frustum being of approximately the same diameter as thebaflle wall 16 so that it abuts at the bases of the triangular passages19 and radial passages 28. It may be held by a nut 41 on an axial bolt42 attached to the end of the central wall 16 by a cross bar 43.

For satisfactory combustion of the oil fuel, a cylindrical combustionchamber 44 with tapering ends 45, 46 is provided, made of a heat andcorrosion resistant stainless steel. Its axis is in line with that ofthe baffie wall 16 and casing 11, and it is closed by a bolted on cover47 at the end remote from the heater. At the other end it joins theheater, the tapering end 46 tapering down approximately to the diameterof the baffle wall 16 and making a gas tight joint with the wall 24. Anentry duct 48 is provided passing through the casing 11 and opening intothe side wall of the combustion chamber through which the oil burner 50fires into the combustion chamber. If it is thought necessary to supplysecondary air, this may be admitted through a manually controlled damperinlet situated below the oil burner entry and be evenly distributed by asmall circular chamber formed round the burner entry.

The end cover 47 being bolted on may be readily removed to gain accessinto the combustion chamber for cleaning.

To reduce heat transfer from the cylindrical wall 44 of the combustionchamber to the casing 11 a light steel shield 49 is located in theannular space between the walls.

The gas to be heated flows from left to right in FIG- URE 1 ie, from theend remote from the combustion chamber towards the combustion chamber sothat the gas at its hottest sweeps over the latter. It is propelled by adirectly electrically driven axial flow fan not shown, but which isaccommodated in an extension of the casing 11 which is preferablyseparately attached as described below with reference to FIGURE 3. Thefan might be mounted at the outflow end but is preferably mounted at theinlet end since this reduces the problems of lubrication and of theelectrical insulation of the driving motor due to heat and also ensuresthat if there is any gas leakage it will be of gas to be heated intocombustion gases and not vice versa.

A considerable degree of regulation of temperature and output may beobtained with the heater shown in FIG- URES 1 and 2 by the use of aregulatable burner and a variable speed motor. Permanent changes may bemade by providing a fan with blades of adjustable pitch or by changingthe fan, which may be a single or multistage fan according to the dutyrequired. Where a larger volume flow and lower temperature rise arerequired this can conveniently be obtained with the construction ofFIGURES 1 and 2, the modification of FIG- URE 3 may be used. Here, inwhich the same references are used for the same parts as in FIGURES 1and 2, the casing 11 is surrounded by a secondary casing 51 spaced fromit to leave an annulus 52 through which a proportion of the gas to beheated is propelled so that it is not directly heated but subsequentlymixes in the ducting which follows the heater with the gas passinginside the casing 11. In this case feet or brackets 13a similar to thefeet and brackets 13 of FIGURES 1 and 2 are secured to end flanges 12aon the casing 51. The whole of the gas to be heated is propelled by thesame axial flow fan 53 here shown at the inlet end, though as mentionedabove it could less desirably be provided at the outlet end. Thediameter of the casing 51 is so chosen in relation to that of the casing11, the flow resistance and the character of flow provided by the fanthat the desired proportions of gas flow inside and outside the casing11. As before the fan may be single or multi-stage and it may haveblades of adjustable pitch and be driven by a variable speed motor. Inthis embodiment, since the casing 11 is cooled by the gas flowing overits outside, the shield 49 of FIGURES 1 and 2 is unnecessary.

In both constructions, the fan and its motor are conveniently mounted ina separate casing such as 54, FIG- URE 3, which can be bolted to the endof the casing 11. The whole assembly can be included in a duct, or ifthe gas to be heated is air which enters at the fan casing an inlet conesuch as 55 may be provided. For safetys sake a narrow duct 56 leading toa pressure relief door of well known type may communicate with thecombustion chamber.

I claim':

1. A continuous type heater for indirectly heating gases comprising anelongated casing of substantially constant cross section, an elongatedtubular Wall forming a main baffle of similar but smaller cross sectionand of shorter length than said casing, and longitudinally disposedwithin said casing spaced therefrom, a corrugated wall in the spacebetween said main baflie and said casing and occupying approximatelythree quarters of the space peripherally and set with its ridges andvalleys longitudinally, its ridges being at least nearly in contact withsaid casing and its valleys being at least nearly in contact with saidmain bafile, said corrugated Wall extending at both ends beyond saidmain bafile but not beyond the ends of said casing, means forming acombustion chamber discharging combustion gases towards one end of saidmain bafiie, said main baflle being imperforate and having thoseportions thereof which face the combustion chamber and face saidcorrugated wall so formed that the combustion gases are directed by itinto the space inside said corrugated wall and outside said main baflle,means at both ends of said corrugated wall closing the ends of the spacebetween said corrugated wall and said main bafiie and therebyrestricting the combustion gases discharged by said combustion chamberto the spaces inside the ridges of said corrugated wall without impedingflow of gas to be heated in the space between said corrugated Wall andsaid casing, and walls defining lateral passages extending radially fromthe space within said corrugated wall and to an opening in said casingfor carrying the combustion gases out of said casing, said passagesbeing located in the space between said main bafiie and said casing inthat part of the periphery not occupied by said corrugated wall andextending substantially over the same length as said corrugated wall,and spaces being left between said walls for the flow of a proportion ofthe gas to be heated.

2. A continuous type heater for indirectly heating gases comprising anelongated casing of substantially constant cross section, an elongatedmain bafile including an irnperforate tubular wall of smaller crosssection and shorter length than said casing and a transverse plateclosing one end of the tubular wall said main bafi le beinglongitudinally disposed Within said casing spaced therefrom all round, acorrugated wall in the space between said bafile and said casing andoccupying the greater part of the space peripherally and set with itsridges and valleys longitudinally, its ridges being at least nearly incontact with said casing and its valleys being at least nearly incontact with said main bat-fie, said corrugated Wall extending at bothends beyond said main battle but not beyond the ends of said casing,means forming a combustion chamber discharging combustion gases towardsthe closed end of said main bafile and so into the space inside saidcorrugated wall and outside said main baflle, means at both ends of saidcorrugated wall closing the ends of the space between said corrugatedwall and said main bafiie and thereby restricting the combustion gasesdischarged by said combustion chamber to the space inside the ridges ofsaid corrugated wall without impeding the flow of gas to be heated inthe space between said corrugated wall and said casing, means closingthe end of the space within said corrugated wall beyond the end of saidmain bafile remote from said combustion chamber, walls defining lateralpassages extending radially from the space within said corrugated walland an opening in said casing for carrying the combustion gases out ofsaid casing, said passages being located in the space between saidimperforate tubular wall and said casing in that part of the peripherynot occupied by said corrugated wall and being located within the samelength as said corrugated wall, said imperforate tubular wallterminating short of said disc and being cut back opposite said lateralpassages to permit outflow of the combustion gases into said passages.

3. A continuous type heater according to claim 2 in which the wallsdefining the lateral passages consist of metal sheets folded into V formwith the valleys so formed extending longitudinally at least near tosaid main battle, the sheets being so shaped and spaced as to leaveradial passages of substantially constant width between them, the heateralso including sheet metal closures extending between the outer edges ofeach V form sheet to complete tubes of substantially triangular sectionalong which the said proportion of the gas to be heated flows.

4. A continuous type heater according to claim 3 in which the lateralpassages extend over the same length as said corrugated wall so thatcombustion gases have access to them from the combustion chamber end,the heater also including bafiles which prevent too great a proportionof combustion gases from taking the short gas path so presented.

5. A continuous type heater according to claim 1 in which said casing ishorizontally disposed and of cylindrical form and said corrugated wallis-made up of metal sheets folded substantially into V form with theirfolds constituting the valleys and their outer edges secured together toconstitute the ridges, a few of the ridges contacting the inside of saidcasing with a sliding fit while the others clear the inside of thecasing thus enabling the wall to be easily inserted and withdrawn.

6. A continuous type heater according to claim 2 having a cylindricalcasing and also comprising a secondary casing surrounding and evenlyspaced from the casing of the heater, said secondary casing extendingbeyond the inlet end of the heater, and an axial flow fan accommodatedin said secondary casing beyond the inlet end of the heater and of adiameter to propel gas to be heated both through the heater and throughthe annulus between the heater casing and secondary casing.

References Cited in the file of this patent UNITED STATES PATENTS1,062,521 Trotter May 20, 1913 1,418,361 Clausing June 6, 1922 1,991,704Schellhammer et al. Feb. 19, 1935 2,214,269 Bryant Sept. 10, 19402,394,627 McCollum et al. Feb. 12, 1946 2,430,227 Jensen et al. Nov. 4,1947 2,482,987 McCollum Sept. 27, 1949

